1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device having an organic thin film transistor.
2. Description of the Related Art
In recent years, various research and development have been conducted on display apparatus having TFT (Thin Film Transistor). Since TFTs are less power consuming and space saving, they have now been started for use as driving transistors for display devices in portable equipments such as mobile phone, notebook type personal computers, and PDAs. Such TFTs are manufactured mostly with inorganic semiconductor materials typically represented by crystalline silicon or amorphous silicon. This is because they can be manufactured by using existent manufacturing steps and manufacturing techniques in semiconductor devices. However, in a case of using the semiconductor manufacturing steps, since the processing temperature upon forming semiconductor films is 350° C. or higher, substrates that can be formed are restricted. Particularly, most of flexible substrates typically represented by plastic materials have a heat resistant temperature of 350° C. or lower and it is difficult to manufacture TFTs of inorganic semiconductor materials by using usual semiconductor manufacturing steps.
In view of the problem, research and development have been conducted on TFT devices using organic semiconductor materials (hereinafter simply referred to as organic TFT) that can be manufactured at a low temperature. Since organic semiconductor films can be formed at a low temperature, the organic TFT can be formed also on a substrate of low heat resistance such as of plastic materials. Accordingly, a new flexible device not found so far can be manufactured.
For the method of forming the organic semiconductor film upon forming the organic TFT, an optimal method is selected for use, depending on the organic semiconductor materials, from a printing method such as inkjet, a rotary coating method, a spray method, a transfer method, a vapor deposition method, a dipping method, or a cast method. For example, a low molecular compound such as a pentacene derivative is deposited as a film by a vapor deposition method or the like, while a high molecular compound such as a polythiophene derivative is deposited from a solution. Examples regarding the method of manufacturing a semiconductor device having the organic thin film transistor include, for example, those in JP-A-2004-80026. In this example, it is constituted to suppress the amount of use of the organic semiconductor material by using a capillary phenomenon.
Recently, research and development have been conducted for further lowering the cost by manufacturing a channel portion of TFT with a small amount of an organic semiconductor material with no loss by using a printing method typically represented by inkjet, micro dispensing, and transfer method. In addition, research and development have also been started for manufacturing also the electrode and the interconnection with the printing method.